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- Angular variation of fire rate of spreadPublication . André, Jorge C. S.; Goncalves, J. C.; Vaz, Gilberto C.; Viegas, Domingos X.Laboratory fire tests were performed in still air, for variable inclinations (10°, 15°) and fuel bed dimensions (1.28 × 2.50–3.0 × 4.6 m2), with homogeneous fuel beds of pine needles and pine wood excelsior. The fire ignition was made at a point, along a closed line with no fuel inside and along a straight edge of the fuel bed. The tests were recorded with an infrared camera and various techniques were developed to implement direct and indirect empirical methods of construction of the ‘orientation function’ of the fire in the given fuel bed and ambient conditions, showing how the rate of spread of a steady straight fire front depends on its orientation on the terrain. The direct method uses a set of straight fire fronts with various orientations whereas the indirect method uses essentially a point ignited fire front. Contrary to what is assumed in BehavePlus model, the orientation function is observed to depend significantly on the properties of the fuel bed. In all tests with closed fire fronts, the full steadiness required by the indirect method was not achieved (namely, at the head of the front), although, for slope angle of 10°, the corresponding errors induced on the orientation function were small.
- Laboratory fire spread analysis using visual and infrared imagesPublication . Martínez-de Dios, J. Ramiro; André, Jorge C.; Goncalves, J. C.; Arrue, Begoña Ch.; Ollero, Aníbal; Viegas, Domingos X.This paper presents an experimental method using computer-based image processing techniques of visual and infrared movies of a propagating fire front, taken from one or more cameras, to supply the time evolutions of the fire front shape and position, flame inclination angle, height, and base width. As secondary outputs, it also provides the fire front rate of spread and a 3D graphical model of the fire front that can be rendered from any virtual view. The method is automatic and non-intrusive, has space–time resolution close to continuum and can be run in real-time or deferred modes. It is demonstrated in simple laboratory experiments in beds of pine needles set upon an inclinable burn table, with point and linear ignitions, but can be extended to open field situations
- Angular variation of fire rate of spreadPublication . André, Jorge C. S.; Goncalves, J. C.; Vaz, Gilberto C.; Viegas, Domingos X.Laboratory fire tests were performed in still air, for variable inclinations (108, 158) and fuel bed dimensions (1.28 2.50–3.0 4.6m2), with homogeneous fuel beds of pine needles and pine wood excelsior. The fire ignition was made at a point, along a closed line with no fuel inside and along a straight edge of the fuel bed. The tests were recorded with an infrared camera and various techniques were developed to implement direct and indirect empirical methods of construction of the ‘orientation function’ of the fire in the given fuel bed and ambient conditions, showing how the rate of spread of a steady straight fire front depends on its orientation on the terrain. The direct method uses a set of straight fire fronts with various orientations whereas the indirect method uses essentially a point ignited fire front. Contrary to what is assumed in BehavePlus model, the orientation function is observed to depend significantly on the properties of the fuel bed. In all tests with closed fire fronts, the full steadiness required by the indirect method was not achieved (namely, at the head of the front), although, for slope angle of 108, the corresponding errors induced on the orientation function were small.
- Parametric study on the performance of an air curtain based on CFD simulations - New proposal for automatic operationPublication . Goncalves, J. C.; Costa, J.J.; Lopes, A.M.G.This paper presents a parametric study on the performance of an air curtain installed over an access door of a refrigerated room. The aim of this work is to quantify, in an integrated way, the influence of the following geometrical and dynamic parameters: door height; temperature difference between rooms, nozzle thickness; initial orientation angle; jet discharge velocity. A numerical model was used to simulate the turbulent non-isothermal 3D airflow generated in the transient period after the door is opened, with the air curtain device turned on or off. Turbulence effects were taken into account with the k-SST model. Results show that the optimum discharge velocity of the air curtain increases with the door height, as well as with the temperature difference between both sides of the air curtain. It was also possible to find an optimum jet nozzle width corresponding to maximum sealing efficiency and lower jet airflow rate. A proposal is made for an empirical correlation to predict the optimum jet discharge velocity as function of the variables used in the parametric study. Additionally, to ensure that the air curtain operates near the optimum conditions, the appropriate air curtain settings are discussed and a new strategy is suggested.
- Laboratory fire spread analysis using visual and infrared imagesPublication . Martínez-de Dios, J. Ramiro; André, Jorge C.; Goncalves, J. C.; Arrue, Begoña Ch.; Ollero, Aníbal; Viegas, Domingos X.This paper presents an experimental method using computer-based image processing techniques of visual and infrared movies of a propagating fire front, taken from one or more cameras, to supply the time evolutions of the fire front shape and position, flame inclination angle, height, and base width. As secondary outputs, it also provides the fire front rate of spread and a 3D graphical model of the fire front that can be rendered from any virtual view. The method is automatic and non-intrusive, has space–time resolution close to continuum and can be run in real-time or deferred modes. It is demonstrated in simple laboratory experiments in beds of pine needles set upon an inclinable burn table, with point and linear ignitions, but can be extended to open field situations.
- A Study on the Sealing Efficiency of Air Curtains: 2D and 3D ApproachesPublication . Goncalves, J. C.; Costa, J.; Figueiredo, R.; Lopes, A.In industrial refrigerated spaces, such as retail stores, where sometimes doors must be open for long periods, the infiltration loads can represent more than half of the total refrigeration load. The use of air curtains can significantly reduce the air infiltration through doorways and, at the same time, it allows the free access by persons and equipment [1]. Besides the experimental research, computational fluid dynamics (CFD) has been commonly used, either adopting a two dimensional (2D) approach [1] or, more recently, through a three-dimensional (3D) perspective [2,3]. This work presents a numerical and experimental study on the performance of air curtain devices in the aerodynamic sealing of access doors of refrigerated spaces. For this propose, a 3D numerical model was developed aiming at the simulation of the turbulent non-isothermal airflow generated by the air curtain since the moment the door is opened. The calculation domain represents a laboratory scale model consisting of two similar adjacent rooms connected by a doorway over which the air curtain device is installed. One of these rooms represents a refrigerated chamber and the other, the outdoor environment. The numerical study was carried out using a commercial CFD code (ANSYS-CFX) and the turbulence effects were approached by k-_SST turbulent model. In the experimental study, the tracer gas technique was used to estimate the air exchange rate through the doorway in the initial period of the transient process and consequently assess the sealing effect obtained with the air curtain device operating at different jet velocities. The numerical results show that the air curtain simulated is appropriate to protect the doorway in its whole width, and a good agreement is verified with the experimental measurements. Results of a simplified 2D approach are also shown and compared with the 3D simulation
- Empirical correlation to estimate the optimum jet velocity of an air curtainPublication . Goncalves, J. C.; Costa, José; Figueiredo, A. Rui; Lopes, AntónioThis paper presents the results of a parametric study to quantify the influence of some thermal and geometrical parameters (door height) on the performance of an Air Curtain Device (ACD). The experimental facility consists of two similar adjacent rooms connected by a door over which the ACD device was installed. The tracer gas technique was used to calculate the sealing effect achieved with the air curtain at different jet velocities. Using a commercial CFD software, a numerical study was also performed to simulate the heat and mass transfer phenomena, as well as the aerodynamic sealing efficiency. A good agreement was observed between experimental and numerical results, showing that the optimum discharge velocity of the ACD air jet increases almost linearly with the door height, as well as with the temperature difference between both sides of the air curtain. It was possible to establish an empirical correlation that predicts reasonably well the optimum discharge jet velocity of a vertical air curtain device, depending on the temperature difference and the doorway height. An electronic device can be included in the ACD enabling the automatic adjustment of the air curtain jet velocity based this correlation, in order to continuously operate close to maximum sealing efficiency.
- Estudo experimental e numérico do escoamento de um jacto plano originado por um dispositivo de cortina de arPublication . Goncalves, J. C.; Costa, José; Figueiredo, A. Rui; Lopes, AntónioNos domínios comercial ou industrial, são muito utilizadas barreiras aerodinâmicas – designadas por cortinas de ar – para confinar ambientes específicos. Neste trabalho apresenta-se o estudo experimental do jacto originado por um equipamento de cortina de ar. Recorrendo à Mecânica de Fluidos Computacional (CFD, foi também realizado um estudo numérico - 3D. Os resultados obtidos por ambas as vias, experimental e numérica, permitiram a caracterização detalhada do escoamento do jacto, sendo coerentes com o esperado para o problema físico em estudo, e coerentes entre si. Um dos aspectos interessantes observados nos ensaios experimentais, foi que o nível de turbulência inicial do jacto se situou sempre abaixo dos 5%, para as diferentes velocidades impostas ao jacto, o que confirma um bom projecto do bocal de descarga